How can I observe notifications triggered by scanning NFC in backgroundMode, I want to customize notifications, add Gif or Image to notification content. because the merchants want to display their images when shopper take their iPhone near goods.
Observe Notification Triggered By Scanning NFC
Your question is not clear. Which notifications are you trying to observe. If you are trying to intercept the system notifications displayed when the device (not your app) encounters a tag, which then requires the user to tap it to launch an app or go to a web site, you cannot do that in a supported way.
If your app wants to display an image when it reads a tag, what you need to do then, is to use background tag reading along with associated domains to launch your app. Then in your app logic, determine if the app has been launched by a tag read, and take the necessary action to show an image.
You can read how to implement this at Adding Support for Background Tag Reading
I also want to add this comment here, because you have been asking the same question many times: this will still need the user to be actively using their phone and respond to prompts for your app to be launched. You cannot implement a way to have your app launched and show images just by having the phone near a tag while not being actively used.